Potential Groundwater Dependent Ecosystem (GDE) Mapping for the Corangamite CMA

Potential Groundwater Dependent Ecosystems (GDE) are ecosystems identified within the landscape as likely to be at least partly dependent on groundwater. State-wide screening analysis was performed to identify locations of potential terrestrial GDEs, including wetland areas. The GDE mapping was developed utilising satellite remote sensing data, geological data and groundwater monitoring data in a GIS overlay model. Validation of the model through field assessment has not been performed. The method has been applied for all of Victoria and is the first step in identifying potential groundwater dependent ecosystems that may be threatened by activities such as drainage and groundwater pumping. The dataset specifically covers the Corangamite Catchment Management Authority (CMA) area. The method used in this research is based upon the characteristics of a potential GDE containing area as one that:\n1. Has access to groundwater. By definition a GDE must have access to groundwater. For GDE occurrences associated with wetlands and river systems the water table will be at surface with a zone of capillary extension. In the case of terrestrial GDE's (outside of wetlands and river systems), these are dependent on the interaction between depth to water table and the rooting depth of the vegetation community.\n2. Has summer (dry period) use of water. Due to the physics of root water uptake, GDEs will use groundwater when other sources are no longer available; this is generally in summer for the Victorian climate. The ability to use groundwater during dry periods creates a contrasting growth pattern with surrounding landscapes where growth has ceased.\n3. Has consistent growth patterns, vegetation that uses water all year round will have perennial growth patterns.\n4. Has growth patterns similar to verified GDEs. \nThe current mapping does not indicate the degree of groundwater dependence, only locations in the landscape of potential groundwater dependent ecosystems. This dataset does not directly support interpretation of the amount of dependence or the amount of groundwater used by the regions highlighted within the maps. Further analysis and more detailed field based data collection are required to support this.\n\nThe core data used in the modelling is largely circa 1995 to 2005. It is expected that the methodology used will over estimate the extent of terrestrial GDEs. There will be locations that appear from EvapoTranspiration (ET) data to fulfil the definition of a GDE (as defined by the mapping model) that may not be using groundwater. Two prominent examples are: 1. Riparian zones along sections of rivers and creeks that have deep water tables where the stream feeds the groundwater system and the riparian vegetation is able to access this water flow, as well as any bank storage contained in the valley alluvials. 2. Forested regions that are accessing large unsaturated regolith water stores.\nThe terrestrial GDE layer polygons are classified based on the expected depth to groundwater (ie shallow 5 m). Additional landscape attributes are also assigned to each mappnig polygon.\n\nIn 2011-2012 a species tolerance model was developed by Arthur Rylah Institute, collaborating with DPI, to model landscapes with ability to support GDEs and to provide a relative measure of sensitivity of those ecosystems to changes in groundwater availability and quality. Rev 1 of the GDE mapping incorporates species tolerance model attributes for each potential GDE polygon and attributes for interpreted depth to groundwater.\n\nSeparate datasets and associated metadata records have been created for GDE species tolerance.

潜在地下水依赖生态系统（Groundwater Dependent Ecosystems, GDE）是指在地表景观中被识别出的、至少部分依赖地下水的生态系统。本研究开展了全州范围筛查分析，以识别潜在陆地地下水依赖生态系统（含湿地区域）的分布点位。该GDE制图依托卫星遥感数据、地质数据与地下水监测数据，通过地理信息系统（GIS）叠加模型构建完成。目前尚未通过野外评估对该模型进行验证。
该方法已在维多利亚州全域应用，是识别可能受排水、地下水抽取等活动威胁的潜在地下水依赖生态系统的首要步骤。本数据集专门覆盖克兰普曼集水区管理局（Corangamite Catchment Management Authority, CMA）管辖范围。
本研究采用的方法基于潜在GDE分布区的以下特征：
1. 具备地下水获取途径。根据定义，GDE必须能够获取地下水。对于与湿地及河流水系相关的GDE而言，地下水位将处于地表，并存在毛细管扩展带。而陆地GDE（湿地与河流水系以外的区域）的地下水获取，则取决于地下水位埋深与植物群落根系深度之间的相互作用。
2. 会在夏季（旱季）利用地下水。受根系吸水的物理特性影响，当其他水源无法获取时，GDE将转而利用地下水——在维多利亚州的气候条件下，这一情况通常出现在夏季。能够在旱季利用地下水的特性，使得这类生态系统与生长已停滞的周边景观呈现出截然不同的生长格局。
3. 生长格局具有持续性。全年利用水源的植被将呈现多年生生长模式。
4. 生长模式与已验证的GDE一致。
当前的制图结果并未体现地下水依赖程度，仅标注了地表景观中潜在地下水依赖生态系统的分布点位。本数据集无法直接解读上述地图中高亮区域的地下水依赖程度或其消耗的地下水量，需开展进一步分析与更细致的野外数据采集工作方可实现此类解读。
本建模所用核心数据的时间跨度大致为1995年至2005年。预计该方法会高估陆地GDE的分布范围：部分区域虽从蒸散发（EvapoTranspiration, ET）数据来看符合本制图模型定义的GDE标准，但实际上可能并未依赖地下水。典型案例包括两类：① 部分河流与溪流沿岸的河岸带，其地下水位较深，但溪流补给地下水系统，河岸植被可直接获取该水流以及河谷冲积层中的岸堤储水；② 依托大量非饱和风化层储水的林区。
陆地GDE图层的面要素根据预期地下水位埋深（即浅埋5米）进行分类，同时每个制图多边形还会被赋予额外的景观属性。
2011-2012年，亚瑟·里尔研究所（Arthur Rylah Institute）与DPI合作开发了物种耐受模型，用于模拟具备支撑GDE能力的景观，并对这些生态系统在地下水可用性与水质变化下的敏感性提供相对量化指标。GDE制图的修订版1（Rev 1）纳入了每个潜在GDE面要素的物种耐受模型属性，以及解译得到的地下水位埋深属性。
目前已针对GDE物种耐受模型创建了独立数据集及相关元数据记录。